1. Field of the Invention
This invention relates to resin-reinforced silicone compositions curable upon exposure to radiation in the electromagnetic spectrum, which compositions when cured demonstrate improved elastomeric properties, such as tensile strength, modulus and elongation. The inventive resin-reinforced silicone compositions may alternatively be rendered curable by exposure to moisture. In addition, the inventive composition may be rendered curable by exposure to radiation in the electromagnetic spectrum, and exposure to moisture. The inventive silicone compositions are particularly well suited for use in electronic conformal coating and potting applications, as well as in automotive gasketing applications, pressure sensitive adhesive applications and the like.
2. Brief Description of Related Technology
Silicone elastomers have been used for potting and encapsulating electrical devices, such as integrated circuits, because of their excellent thermal stability, low temperature flexibility and high dielectric strength. They typically provide shock, vibrational and thermal stress protection on fragile electronic components. [See U.S. Pat. Nos. 3,933,712; 4,072,635; 4,087,585; 4,271,425; 4,374,967; and D. Dickson, Jr., Proc. Electric/Electronic Intel. Conf., 12, 92 (1975). See also U.S. Pat. No. 4,374,967.]
Certain silicones containing (meth)acrylate functional groups may be cured by ultraviolet light (xe2x80x9cUV lightxe2x80x9d). See U.S. Pat. Nos. 4,201,808 and 4,348,454, and U.K. Patent Application GB 2039287A, which, though not producing elastomeric materials, describe UV light curing compositions of silicones containing (meth)acrylates for paper release coatings.
Room temperature vulcanization (xe2x80x9cRTVxe2x80x9d) (also called moisture curable) silicone compositions are well known, such as those sold under the ULTRA tradename.
Loctite Corporation has for a number of years sold under the xe2x80x9cNUVASILxe2x80x9d tradename a variety of UV and UV/moisture curable silicone compositionsxe2x80x94that is, silicone compositions curable upon exposure to UV light or UV light, followed by exposure to moisture. These compositions generally provide a reactive polyorganosiloxane component, and a photoinitiator component. Where moisture cure capabilities are also desirable, a moisture cure catalyst is also included. The viscosity of the composition, as well as the physical properties of the cured elastomer, may be modified by the inclusion of a non-reactive silicone fluid, such as a polydimethyl siloxane, for instance one terminated with alkyl silyl groups (e.g., trimethyl silyl, hydroxyl dimethyl silyl, alkoxy dimethyl silyl and the like). See U.S. Pat. No. 4,528,081 (Lien), the disclosure of which is hereby expressly incorporated herein by reference. See also U.S. Pat. No. 5,179,134 (Chu) and U.S. Pat. No. 5,300,608 (Chu), the disclosure of each of which is hereby expressly incorporated herein by reference.
Other UV and UV/moisture curable silicone compositions are also known. [See U.S. Pat. No. 5,489,622 (Hara) and U.S. Pat. No. 5,384,340 (Hara).]
Silicone elastomers, however, are inherently very weak materials due to weak intermolecular van der Waals forces between the siloxane chains. In the past, improved strength has been imparted to certain of these compositions by including a fumed silica as a reinforcing filler. See U.S. Pat. No. 4,675,346 (Nakos), the disclosure of which is expressly hereby incorporated herein by reference. One drawback to this approach in some instances is that dispensability may become difficult, as oftentimes even a small amount of fumed silica tends to increase viscosity.
In addition, inclusion of such reinforcing filler tends to confer a translucent or xe2x80x9cmilkyxe2x80x9d appearance to the silicone compositions. Such an appearance can be disadvantageous in many applications, particularly where cure is to occur through exposure to radiation in the electromagnetic spectrum and/or where clarity of the cured elastomer is a desirable property. Radiation cure may become impeded when the composition has a translucent appearance because the radiation pathway through the composition may become blocked.
Recently, Loctite Corporation made an advance in the field of anaerobically-curable silicone compositions by providing compositions including (a) a silicone fluid formed as the reaction product of a first silane having at least one hydrolyzable functional group, and a second silane having a (meth)acrylic functional group and at least one hydrolyzable meth)acrylic functional group and at least one hydrolyzable functional group. (b) a (meth)acrylate monomer; and (c) polymerization initiator. See U.S. Pat. No. 5,605,999 (Chu) and U.S. Pat. No. 5,635,546 (Rich), the disclosures of each of which are hereby expressly incorporated herein by reference.
Silicone products of the type noted above (sometimes referred to as xe2x80x9cMQxe2x80x9d resins) have been used to impart reinforcement properties to cured elastomers of heat-curable silicone compositions without increasing the viscosity of the composition, and while maintaining the clarity of the composition.
MQ resins generally are copolymers of siloxanes formed from reactive trialkylsilyl (xe2x80x9cMxe2x80x9d) and tetra functional silicate (xe2x80x9cQxe2x80x9d) structures that can be prepared by either cohydrolyzing silanes containing M and Q units or by silylating inorganic silicates with a trialkylsilyl containing silanes.
Vinyl- or hydride-containing silanes have been added during preparation to yield MQ resins suitable for use in heat-cure silicone compositions. During heat cure, the vinyl groups on the MQ resin and the silicone fluid polymerize in a crosslinked network with the MQ resin incorporated in the network for reinforcement.
MQ resins have been used to impart reinforcement properties to room temperature vulcanization (xe2x80x9cRTVxe2x80x9d) silicone compositions, as well. See U.S. Pat. No. 5,340,887 and European Patent Document EP 767 216. Here, the use of a resin-polymer system is described where both resin and polymer contain hydroxl groups and may be crosslinked with the addition of an oxime crosslinker.
One drawback to the use of MQ resins to reinforce reaction products of silicone-based compositions is their compatibility with the remaining components of the compositionxe2x80x94that is, phase separation is oftentimes seen to occur. This results in a compromised shelf life stabiliity for certain one-part silicone-based compositions.
Notwithstanding the state-of-the-technology, it would be desirable to provide resin-reinforced radiation and radiation/moisture curable silicone compositions. Such compositions could advantageously be used in a variety of commercial applications and would benefit from the enhanced strength imparted by the resin reinforcement.
The present invention meets the desires discussed above by providing resin-reinforced silicone compositions capable of curing upon exposure to radiation in the electromagnetic spectrum, such as UV light, and exposure to moisture, such as is found under atmospheric conditions, and a combination thereof:
The compositions include:
(a) a polyorganosiloxane, having photocurable groups, such as (meth)acrylate or glycidoxyl functionality, like methacryloxypropyl, vinyl ether groups and the like and/or moisture curable groups, such as alkoxy or aryloxy groups, like methoxy, acetoxy groups, oximino groups, enyloxy groups, imido groups, amino groups, and the like;
(b) a silicone resin selected from
(i) those formed from at least one silane within the formula R1mR2pSi(X)4xe2x88x92(m+p) I, where R1 is a (meth)acrylate functional group or a hydrolyzable group, and R2 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 alkylaryl, or a hydrolyzable group, X is a hydrolyzable group, m is an integer from 1 to 3, and m+p is an integer from 1 to 3;
(ii) those formed from at least one silane within the formula R3qSi(X)4xe2x88x92q II, where R3 may be the same as or different from R2 above and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, and C7-19 alkylaryl, and q is an integer from 1 to 3, reacted with at least another silane within the formula of R4rR5sSi(X)4xe2x88x92(r+s) III, where R4 and R5 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 alkylaryl, r is an integer from 1 to 3, and r+s is an integer from 1 to 3, provided the silicone resin formed contains at least some hydrolyzable group, X; and combinations thereof; and
(c) a photoinitiator, moisture cure catalyst, and combinations thereof.
In a particularly desirable aspect of the invention, the compositions include:
(a) a polyorganosiloxane, having photocurable groups, such as (meth)acrylate functionality, like methacryloxypropyl, and/or moisture curable groups, such as alkoxy or aryloxy groups, like methoxy;
(b) a silicone resin formed as the reaction product of:
(i) at least one silane within the formula R1mR2pSi(X)4xe2x88x92(m+p) I, where R1 is a (meth)acrylate functional group or a hydrolyzable group, and R2 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl, or a hydrolyzable group, X is a hydrolyzable group, m is an integer from 1 to 3, and m+p is an integer from 1 to 3, and
(ii) at least one other silane within the formula RnSi(X)4xe2x88x92n IV, where R may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl, haloalkyl, and haloaryl, X is a hydrolyzable functionality, and n is an integer of from 0 to 3; and
(c) a photoinitiator, a moisture curing catalyst, and combinations thereof.
The invention further provides a process for preparing reaction products from the compositions of the present invention, the steps of which include applying the composition to a desired substrate surface, particularly one having shadow areas not readily accessible to light, and irradiating the coated substrate surface to conditions which are appropriate to effect cure thereofxe2x80x94e.g., exposure to radiation in electromagnetic spectrum. Optionally, the composition may then be exposed to moisture to further cure the composition.
Also, the invention of course provides the reaction products so-formed by the above-described process, which reaction products demonstrate improved physical properties, such as tensile strength, modulus and elongation.
The present invention will be more fully appreciated by a reading of the detailed description and the illustrative examples which follow thereafter.
As noted above, the compositions include:
(a) a polyorganosiloxane, having photocurable groups, such as (meth)acrylate functionality, like methacryloxypropyl, and/or moisture curable groups, such as alkoxy or aryloxy groups, like methoxy;
(b) a silicone resin selected from
(i) those formed from at least one silane within the formula R1mR2pSi(X)4xe2x88x92(m+p) I, where R1 is a (meth)acrylate functional group or a hydrolyzable group, and R2 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 alkylaryl, or a hydrolyzable group, X is a hydrolyzable group, m is an integer from 1 to 3, and m+p is an integer from 1 to 3;
(ii) those formed from at least one silane within the formula R3qSi(X)4xe2x88x92q II, where R3 may be the same as or different from R2 above and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 alkylaryl, and q is an integer from 1 to 3, reacted with at least another silane within the formula of R4rR5sSi(X)4xe2x88x92(r+s) III, where R4 and R5 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 alkylaryl, r is an integer from 1 to 3, and r+s is an integer from 1 to 3, provided the silicone resin form contains at least some hydrolyzable group, X; and combinations thereof; and
(c) a photoinitiator, a moisture catalyst, and combinations thereof.
In a particularly desirable aspect of the invention, the compositions include:
(a) a polyorganosiloxane, having photocurable groups, such as (meth)acrylate functionality, like methacryloxypropyl, and/or moisture curable groups, such as alkoxy or aryloxy groups, like methoxy;
(b) a silicone resin formed as the reaction product of:
(i) at least one silane within the formula R1mR2pSi(X)4xe2x88x92(m+p) I, where R1 is a (meth)acrylate functional group or a hydrolyzable group, and R2 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl, or a hydrolyzable group, X is a hydrolyzable group, m is an integer from 1 to 3, and m+p is an integer from 1 to 3, and
(ii) at least one other silane within the formula RnSi(X)4xe2x88x92n IV, where R may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl, haloalkyl, and haloaryl, X is a hydrolyzable functionality, and n is an integer of from 0 to 3; and
(c) a photoinitiator, a moisture curing catalyst, and combinations thereof.
The inventive compositions may be used as adhesives, coatings, sealants, as well as molding compounds, in applications ranging for instance from preapplied gasketing applications, to virtually any existing RTV silicone application that can accommodate a UV light cure step.
The inventive compositions are capable of being rapidly cured by exposure to UV light, and if desired exposure to atmospheric moisture. Cure typically occurs through exposure to light with a UV intensity of 70,000 mW/cm2. The cured compositions are tough elastomeric materials that display typical silicone elastomer properties including wide usable temperature range, and good water resistance.
The polyorganosiloxane should have an average linear molecular size of at least about 50 siloxane units, with (meth)acrylate, (meth)acryloxyalkyldialkoxysilyl and/or (meth)acryloxyalkyldiaryloxysilyl groups on the polyorganosiloxane, such as at the terminal ends. Desirably, the (meth)acryloxyalkyldialkoxysilyl group should be a (meth)acryloxypropyldimethoxysilyl group.
For instance, the polyorganosiloxane may be selected from compounds within formula V below: 
where R6, R7, R8 and R9 may be the same or different and are alkyl, alkenyl, aryl, (meth)acryl, and the like, provided that at least one of R6, R7, R8 and R9 is (meth)acryl, having up to carbon atoms (C1-10), or substituted versions thereof, such as halo- or cyano-substituted; R10 is alkyl having up to 10 carbon atoms (C1-10); n is an integer between about 100 and 1,200; a is 1 or 2; b is 0, 1 or 2; and a+b is 1, 2 or 3.
It is particularly desirable to hare polyorganosiloxanes, where R6 and R7 are methyl, R8 is (meth)acrylate; R9 and R10 is alkyl, such as methyl, and n is an integer between about 100 and 1,200, inclusive.
Generally, it is convenient to use a linear polyorganosiloxane having (meth)acrylate groups terminating the silicone. Such (meth)acrylate-terminated silicones may be represented by the formula VI below: 
where R6 and R7 are as defined above, MA is (meth)acrylate and c is 0, 1 or 2.
Generally, the silicone resins are a family of silicone-based materials with a structure represented generally by (R3SiO1/2)w(R2SiO2/2)x(RSiO3/2)y(SiO4/2)z, where a portion of the total R content includes (meth)acrylate functionality. Desirably, and in the aspect of the invention where at least two silanes form a reaction product, the total (meth)acrylate containing silicon functionality on the silicone resin may be up to about 15 mole % of the silicone resin, such as in the range of about 1 mole % to about 10 mole %, for instance about 4 mole % to about 8 mole %.
Silicone resins may be formed from at least one silane within the formula R1mR2pSi(X)4xe2x88x92(m+p) I, where R1 is a (meth)acrylate functional group or a hydrolyzable group, and R2 may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-12 alkyl, C6-12 aryl, C7-18 arylalkyl, C7-18 alkylaryl, or a hydrolyzable group, X is a hydrolyzable functionality, m is an integer of from 1 to 3 and m+p is an integer from 1 to 3, or as reaction products of that at least one silane and at least one second silane within the formula RnSi(X)4xe2x88x92n II, where R may be the same or different and may be selected from monovalent ethylenically unsaturated radicals, hydrogen, C1-2 alkyl, C6-12 m aryl, C7-18 arylalkyl, C7-18 alkylaryl, haloalkyl, and haloaryl, X is a hydrolyzable functionality, and n is an integer of from 0 to 3. Certain of these moieties ordinarily may be reaction products of halogenated trialkylsilanes, tetraalkoxysilanes and (meth)acrylate substituted trialkoxysilanes.
The silicone resins may be formed through hydrolysis and condensation reactions.
These silicone resins may also be prepared by (1) acidifying water-soluble sodium silicate, and thereafter capping the resulting sol with a trialkylsilyl group as well as with (meth)acrylate-containing silane or (2) co-hydrolyzing and/or co-condensing silanes containing trialkylsilane groups, vinyl silane groups and tetraalkoxysilane. For a further discussion of silicone resins generally, see R. H. Blaney et al., xe2x80x9cSilsesquioxanesxe2x80x9d, Chem. Rev., 95, 1409-30 (1995).
In the reaction forming such silicone resins, a first silane should be used in an amount within the range of from about 1 to about 10 mole %, such as from about 4 to about 8 mole % of the combination of the first and second silanes. The other silane(s) should be used in an amount with the range of from about 90 to about 99 mole %, such as from about 92 to about 96 mole % of the combination of the first and the other silanes.
In the compositions of the present invention, the hydrolyzable functionality in the silanes may be any functionality which, when attached to a silicon atom through a Sixe2x80x94O, Sixe2x80x94halo, Sixe2x80x94N or Sixe2x80x94S bond, is readily hydrolyzable in the presence of water. Examples of such functionality include, but are not limited to, halogen (meth)acryloxy, alkoxy, aryloxy, isocyanato, amino, acetoxy, oximinoxy, aminoxy, amidato and alkenyloxy.
In the compositions of the present invention, R may be chosen from C1-12 alkyl, C6-12 aryl, alkenyl, (meth)acryloxyalkyl and vinyl. In such instances, when R is C1-12 alkyl or C6-12 aryl, examples of the first silane include, but are not limited to, (meth)acryloxypropyl trimethoxysilane, (meth)acryloxypropyl trichlorosilane, (meth)acryloxypropyl dimethylchloro silane, (meth)acryloxymethyl dichlorosilane and (meth)acryloxymethyldimethyl acryloxysilane.
When R1 on the other silane is chosen from C1-12 alkyl, C6-12 aryl, the other silane itself may be dimethylchlorosilane, phenyltrichlorosilane, tetrachlorosilane, trimethylchlorosilane, trimethylmethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane and tetraethoxysilane.
Of course, appropriate combinations of the first silane may be used as the first silane component; likewise appropriate combinations of the other silane(s) may be used as the other silane component.
The photoinitiator may include any one of those known in the art to initiate the curing of (meth)acrylate functional groups. These photoinitiators include benzoin and substituted benzoins, benzophenone, Michler""s ketone, dialkoxyacetophenones, such as diethoxyacetophenone, and the like. Generally, the amount of photoinitiator chosen should be within the range of from 0.1 to about 5% by weight.
In those compositions in which moisture cure capabilities are also present, a moisture cure catalyst should also be included in an amount effective to cure the composition. For example, from about 0.1 to about 5% by weight, such as about 0.25 to about 2.5% by weight, of the moisture cure catalyst is desirable. Examples of such catalysts include organic titanium, tin, and zirconium complexes and of course combinations thereof. Tetraisopropoxytitanium and tetrabutoxytitanium are particularly desirable. See also U.S. Pat. No. 4,111,890, the disclosure of which is expressly incorporated herein by reference.
The compositions may also include a diluent component reactive at elevated temperature conditions.
Reactive diluents include those materials which are particularly (1) unreactive at ambient temperature conditions and (2) reactive at elevated temperature conditions. In addition, such diluents should be capable of not only reacting with other components of the inventive adhesive compositions, but also with reactive moities on itself. This feature allows the diluent to self-polymerize as well as polymerize with reactive moities on the other components of the composition. As such, the reactive diluent becomes incorporated into the polymeric matrix which forms at ambient temperature and which further forms at increased temperatures. The incorporation of the reactive diluent provides at least in part for the high temperature performance demonstrated by the cured composition.
More specific examples of such reactive diluents include alkenyl- or alkynyl-terminated silicone fluids, an example of which is vinyl-terminated polydimethylsiloxane.
Other examples of reactive diluents based on silicone fluids include alkenyl- or alkynyl-terminated silicone resins.
And of course appropriate combinations of such reactive diluents may be used.
When used, the reactive diluent should be employed in an amount within the range of about 1 to about 50% by weight, based on the total weight of the composition.
The compositions of the invention may also include other constituents to modify the physical properties of the composition or reaction products thereof, as desired depending on the specific application for which a composition within the scope of this invention is destined for use. For instance, adhesion promoters, such as (meth)acryloxypropyltrimethoxysilane, trialkylisocyanurate, and the like, may be included in an amount of up to about 5% by weight. Conventional silicone fillers, such as fumed and precipitated silica [see e.g. U.S. Pat. No. 4,675,346 (Nakos)], iron oxide, barium zirconate and calcium carbonate, may also be included in the inventive compositions. Still other conventional additives may also be included in the inventive compositions, such as non-(meth)acrylate functionalized silicone diluents (including silicone fluids having viscosities of between about 100 and 1,500 cps, which may or may not be terminated with hydrogen, alkyl, alkenyl, alkoxy or hydroxyl functionality, such as trimethylsilyl groups) and plasticizers, each of which may be present in an amount of up to about 30% by weight.
The plasticizers may be chosen from a wide variety of plasticizers depending on the desired properties of the composition and/or reaction product thereof. See e.g., U.S. Pat. No. 3,794,610 (Bachmann), the disclosure of which is hereby expressly incorporated herein by reference.
The compositions of the present invention may be prepared using conventional methods that are well known to those persons of skill in the art. For instance, the components of the inventive compositions may be mixed together in any convenient order consistent with the roles and functions the components are to perform in the compositions. Conventional mixing techniques using known apparatus may be employed.
The invention also provides a process for preparing reaction products from the compositions of the present invention, the steps of which include applying the composition to a desired substrate surface and exposing the coated substrate surface to conditions which are appropriate to effect cure thereofxe2x80x94e.g., exposure to radiation in the electromagnetic spectrum.
Also, the invention of course provides reaction products so-formed by the above-described process, which reaction products demonstrate improved physical properties, such as tensile strength, modulus and elongation.
In view of the above description of the present invention, it is clear that a wide range of practical opportunities is provided.
The following examples are illustrative of the invention, but in no way are intended to limit its scope.